Variable polarization saturable magnetic circuits



a. JACQUQT 3,255,369

VARIABLE POLARIZATION SATURABLE MAGNETIC CIRCUITS June 7, 1966 2 Sheets-Sheet 1 Filed June 17. 1960 lNvEN TOR BERNARD JAGOUOT June 7, 1966 B. JACQUOT 3,255,369

VARIABLE POLARIZATION SATURABLE MAGNETIC CIRCUITS Filed June 17. 1960 2 Sheets-Sheet 2 United States Patent 3,255,369 VARIABLE POLARIZATION SATURABLE MAGNETIC CIRCUITS Bernard Jacquot, Orsay, France, assignor to Commissariat a lEnergie Atomique, Paris, France, an organization of France v Filed June 17, 1960, Ser. No. 36,855 Claims priority, application France, June 20, 1959,

798,089 4 Claims. (Cl. 313-63) ties used in accelerators of electrically charged particles.

The chief object of this invention is to provide a circuit of this kind such that the magnetic flux generated by its coil is better distributed in the core thereof.

The essential feature of this invention consists in giving the cross section area of the core of such a circuit a value which is greater in the portion thereof surrounded by the coil than in at least the portion thereof remotest from the coil.

Other features of this invention will be more explicitly described hereinafter.

Before describing the invention itself, the following explanations should be given.

It is often necessary, when resonant circuits are used, to be able to tune these circuits to a wide band of frequencies.

nite but may have any value within a band of several octaves, for instance for teleguiding missiles.

Up to the present time, in order to tune such resonating circuits, use was made of mechanical methods based upon the variation either of a capacity or of an inductance. Such methods permit of obtaining good Q factors (low losses) but they are slow and only permit of covering a narrow frequency band.

Electrical methods are also being used which make use either of variations of permitivity of the dielectric of the capacitor or of variations of the permeability of the magnetic circuit of a self-inductance device.

The first of these electrical methods permits of covering only a narrow band (about one octave), the power being always relatively low.

On the contrary, the variation, by magnetic polarization of the permeability of a material (preferably a ferrite) constituting the magnetic circuit of a self-inductance device makes it possible to vary the inductance thereof in a ratio which may reach several hundreds. But in apparatus based upon this principle:

Either the magnetic circuit is surrounded over its whole length (or at least over a great length) by a helical coil through which the variable polarization current flows, which is very inconvenient for maintenance and for changes of utilization, especially when the circuit consists of groups of frames or rings;

Or the magnetic circuit is surrounded only over a small length by the coil and, in this case, the inductance lines partly close on the outside of the circuit proper, in particular for high values of the polarization current, which requires a current consumption higher than that necessary in the preceding case. In particular, if the value of the polarization circuit is increased, saturation takes place in the vicinity of the inductance coil before the induction reaches the desired value at other points.

According to the present invention, the cross section area of the magnetic circuit is increased inside the polarization coil so that the saturation is greater in this portion of the circuit, which improves the distribution of the flux and correspondingly reduces the necessary consumption of polarization current.

In the preferred embodiment of this invention, this increase is obtained by adding to the magnetic circuit of constant or substantially constant cross section an element or a plurality of elements of ferromagnetic material capable of distributing the magnetic flux along this circuit. For the sake of simplicity, this element or plurality of elements will be hereinafter designated by the term distributor.

Of course, if the circuit is the magnetic circuit of the self-inductance means of a resonant circuit or more generally if an alternating field is superimposed on the polarization magnetic field, the ferromagnetic material that is used must have losses as low as possible. Laminated elements will be used for this purpose.

The various sections of the distributor may be chosen in such manner that saturation begins in the various sections of the magnetic circuit for practically equal values of the polarization current. In other words, if the cross sectional area of the distributor is maximum inside the coil, it decreases the quicker at the level of every cross section as the flux loss to be compensated for at this level is greater.

The shape of the distributor may be the simpler as greater variations can be accepted for the polarization flux passing through the various cross sections of the magnetic circuit.

The distributor conveys the magnetic flux of the polarization coil to the portion of the circuit where this flux would be supplied only insufiiciently if said distributor did not exist. In particular, when the portion of the circuit surrounded by the coil is saturated, if the distributor did not exist it would be practically useless to increase the polarization current to saturate the opposed portion of the circuit, since the induction lines would close in air and not in the circuit. It would therefore be practically impossible, in the case of the magnetic circuit of a self-inductance device, to obtain for its inductance the value corresponding to complete saturation of said conduit.

Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, which;

FIG. 1 diagrammatically shows in elevational view a magnetic circuit made according to the invention.

FIG. 2 is a similar view relating to a modification.

FIG. 3 is a diagrammatic sectional view of an accelerating inductive cavity resonator device provided with magnetic circuits made according to the invention.

FIG. 4 shows an electric lay-out equivalent to this cavity resonator device.

FIGS. 5 and 6 show such a cavity, respectively in cross sectional view and in perspective view.

FIG. 7 shows curves illustrating some properties of this cavity resonator device.

The magnetic circuits illustrated by FIGS. 1 and 2 each comprises a core 1 of magnetic material closed upon itself. This core, the cross section area of which is congiven merely by way of example and in stant over its whole length, is in the form of a circular ring in FIG. 1 and of a rectangular frame in FIG. 2. It is surrounded over a small length thereof by a polarization coil 2 and a distributor 3 is fixed to core 1 therealong symmetrically with respect to the transverse plane of coil 2. In FIG. 1, distributor 3 is in the form of a crescent and in FIG. 2 it is in the form of a U having pointed branches. The central portion of distributor 3 is located within said coil 2.

In the embodiment illustrated by FIGS. 3 to 6, a magnetic circuit of this kind is used in a high frequency selfinductance device 4 included in an inductive cavity resonator device serving to the acceleration of protons in a synchrotron.

In such an apparatus, the protons describe a closed trajectory in an annular vacuum chamber 5 and are accelerated on every passage by a difference of potential of suitable direction applied between two electrodes 6 and 7 limiting and insulating gap 8 (or accelerator gap) of this chamber.

Instead of directly applying to these electrodes the electric voltage created by a high frequency generator of high electromotive force, it is preferred, in order to reduce the constant energy, to insert these electrodes in a resonant circuit including self-inductance means 4 and a capacity 9 excited by a high frequency generator 10 the power of which may be much lower than if the electric voltage was directly applied to the electrodes.

-The acceleration frequency must vary, in accordance with the synchrontron principle, with the energy of the accelerated protons and resonant circuit 49 must be capable of being tuned, same as generator 10, within the whole corresponding frequency band.

By way of indication, in the Saturne proton synchrotron of Saclay (France), this frequency band ranges from 0.75 to 8.5 megahertz. The ratio of the extreme frequencies to each other is therefore higher than 11 and it is necessary to be able to vary the values of self-inductance means 4 and/or of capacitor 9 in a ratio of about 130 (equal to the square of the ratio of the extreme resonance frequencies). Therefore, if the capacity of capacitor 9 may vary from 1 to 4, the self-inductance means must vary from 1 to 35.

The self-inductance means 4 illustrated by FIGS. 3 to 6 are symmetrical with respect to the ground and consist of two coaxial lines disposed in line with each other, each around a portion of the trajectory of the protons contiguous to accelerator gap 8. The opposed ends of these lines are short-circuited by end elements 11 and, at their opposed ends, their outer conductors are assembled together, thus constituting the outer wall of the cavity, whereas their inner conductors, insulated from each other, form two portions of annular chamber 5 ending respectively at the edges 6 and 7 of the above mentioned gap.

This self-inductance device 4 is made variable by means of magnetic cores 1 of ferrite housed between the outer conductors of every coaxial line, these cores being polarizable by coils 2 and being provided with distributor 3 for the purpose above described.

In a practical construction of the inductive resonator device which proved very satisfactory and which is illustrated by FIGS. 5 and 6:

The external conductor common to both of the coaxial lines and which constitute the outer wall of the cavity consists of four plates 4 of mild steel (forming a magnetic shielding) covered on both of their faces with copper (ensuring electrical conductivity), the whole forming a rectangular parallelepipedal 1.90 m. long, 1 m. wide .and 0.70 m. high.

The inner conductors consist of two tubes of relatively flat cross section 4 made of stainless steel, having a width of 450 mm. and a height of 134 mm.;

At the place of the accelerator gap, an insulating joint 12 is provided, consisting of the material known under the trademark name Araldite extending over a length of 55 mm. and fixed in gastight fashion to the edges of tubes 4 Tubular elements 4,, extend through the ends 11 of the cavity and their portions on the outside of said cavity are connected through flexible diaphragm means to the remainder of the vacuum chamber;

Magnetic core 1 is formed by forty rectangular frames of a ferrite designated by the trademark name Fernilite 1101 the inner dimensions of which are 553 mm. x 200 mm. and the outer dimensions of which are 800 mm. X 447 mm., with a thickness of 25 mm. Each of these frames consists of the assembly of two long bars 13 and two short bars 14. These frames are grouped two by two and the whole of these frames is held by means of removable fixation elements 15 carried by a rigid structure 16 provided in the cavity. Large intervals 17 are provided between the pairs of frames so as to permit cooling thereof;

Polarization of the core is performed by the current circulating in two coils 2 which extend over only a small length of the ferrite frames, these coils being disposed symmetrically with respect to the middle transverse plane of the cavity, on the inside thereof and on one side only of the vacuum chamber. In order to uncouple the low frequency polarization field from the high frequency accelerating field, coils 2 are twisted in the form of an 8. For this purpose, the frames of every half cavity are grouped ten by ten and the turns of coils 2 are wound successively in opposed directions about every group of ten frames. This arrangement permits of practically reducing to zero the undesirable induced electromotive forces. Every coil consists of ten copper tubes having a square external cross section cooled by a water circulation. The total inductance of these coils averages 5 mh. and the maximum intensity of the current that can flow therethrough is about 400 A. A device for filtering the polarization current is provided on the outside of the cavity to avoid any leak of high frequency parasitic inductions toward the remainder of the system;

The distributor elements 3 are bars fixed on the sides of the ferrite frames and extending through coils 2. These bars are 447 mm. long and have a square cross section the side of which is 50 mm. They are laminated and constituted by mild steel sheets 0.5 mm. thick, glued against one another by means of the material known under the trademark name Araldite.

The curves of FIG. 7 permit of understanding the advantage resulting from the presence of distributor element 3.

The tuning frequencies of the cavity resonator device are plotted in ordinates, in Megahertz, the intensity of the polarizing current is plotted in abscissas, in a-mperes, the capacity being supposed to be maintained at its value at the end of every cycle.

Curve 18 relates to the case of a polarization winding uniformly distributed around the frames. The tuning frequency reaches 8.4 megahertz with a polarizing current of 184 A.

Curve 19 corresponds to the case where the polarization coil is localized but the magnetic circuit is not provided with a distributor. It is necessary to have a polarizing current of 460 A. to reach the frequency of 8.4 megahertz.

Finally, curve 20 corresponds to the case above described of a localized coil in combination with distributor elements. A polarizing current of 229 A. sufiices to obtain the frequency of 8.4 megahertz.

A more elaborated shape of the distributing elements would permit of obtaining a curve 20 closer to curve 18 and thus to reduce the necessary polarizing current.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. A variable polarization saturable magnetic circuit which comprises in combination a magnetic core closed upon itself and a polarizing coil surrounding only a portion of said core, said core comprising a first element of uniform cross-sectional area over its whole length and an open ended second element fixed to the first one in juxtaposed relation thereto along a portion thereof including that located within said coil, so that the total cross-sectional area of said core decreases from the portion located in said coil to that remotest from said coil.

2. A variable polarization saturable magnetic circuit according to claim 1 wherein said first element of said core is in the form of a rectangular frame the four sides of which are of the same cross-sectional area, one side of said frame being surrounded by said coil, and wherein said second element of said core consists of a bar of magnetic material juxtaposed to said frame side surrounded by said coil.

3. A magnetic circuit according to-claim 2 wherein said frame is made of ferrite and said bar of mild steel.

4. A synchrotron comprising a cavity resonator for ac- 25 celerating protons, said cavity resonator including a mag- References Cited by the Examiner UNITED STATES PATENTS 1,644,729 10/1927 Johannesen 336-212 2,454,094 11/ 1948 Rosenthal 313-62 X 2,581,819 4/1954 Strandberg 313-62 X 2,675,470 4/ 1954 Wilderoe 313-62 X 2,765,448 10/ 1956 Dutfing 336-229 X 2,799,822 7/1957 Dewitz 336-229 X HERMAN KARL SAALBACH, Primary Examiner.

RALPH G NILSON, A. GAUSS, GEORGE N. WESTBY,

Examiners.

V. LAFRANCHI, S. CHATMON, JR.,

Assistant Examiners. 

1. A VARIABLE POLARIZATION SATURABLE MAGNETIC CIRCUIT WHICH COMPRISES IN COMBINATION A MAGNETIC CORE CLOSED UPON ITSELF AND A POLARIZING COIL SURROUNDING ONLY A PORTION OF SAID CORE, SAID CORE COMPRISING A FIRST ELEMENT OF UNIFORM CROSS-SECTIONAL AREA OVER ITS WHOLE LENGTH AND AN OPEN ENDED SECOND ELEMENT FIXED TO THE FIRST ONE IN JUXTAPOSED REALTION THERETO ALONG A PORTION THEREOF INCLUDING THAT LOCATED WITHIN SAID COIL, SO THAT THE TOTAL CROSS-SECTIONAL AREA OF SAID CORE DECREASES FROM THE PORTION LOCATED IN SAID COIL TO THAT REMOTEST FROM SAID COIL. 